1. Field of the Invention
The present invention relates to a production method of a wired circuit board and, more particularly, to a production method of a flexible wired circuit board.
2. Description of the Prior Art
In the production method of the flexible wired circuit board, the subtractive process and the additive process are known as the patterning process of a wiring circuit pattern. Of these patterning processes, the additive process is advantageous to the forming of a high-definition pattern required for a liquid crystal display part of electronic equipment such as a mobile phone.
As described for example by JP Laid-open (Unexamined) Patent Publication No. 2003-37137, the additive process is known as a process of forming a conductor pattern on an insulating substrate. Specifically, according to this additive process, a first conductor layer of a thin metal film is formed on an entire surface of an insulating substrate, then the first conductor layer is covered with a plating resist so that a conductor pattern is exposed from the plating resist, then a second conductor is formed on an surface of the first conductor layer not covered with the plating resist, then the plating resist is removed, and finally a portion of the first conductor layer on which the second conductor layer was not formed is removed by etching, to thereby form the conductor pattern.
However, the additive process described above causes the plating resist 22 formed on the first conductor 21 on the insulating substrate 26 to form, at a bottom thereof contacting with the first conductor 21, a skirt portion 23 that becomes wider toward the lower side gradually, as shown in FIG. 2(a). This produces the result that when the second conductor 24 is formed on a surface of the first conductor 21 not covered with the plating resist 22, as shown in FIG. 2(b), and thereafter the plating resist 22 is removed, as shown in FIG. 2(c), an undercut portion 25 that becomes narrower toward the lower side gradually is formed at a bottom of the second conductor 24 contacting with the first conductor 21 due to the skirt portion 23. This in turn produces the result that when the first conductor 21 is removed by etching, the first conductor 21 on the bottom of the second conductor 24 is etched to be largely scooped out inwardly of the second conductor 24 due to the undercut portion 25, as shown in FIG. 2(d). This produces the disadvantage that the adhesiveness between the insulating substrate 26 and the first conductor 21 is reduced significantly so that the conductor pattern comprising the first conductor 21 and the second conductor 24 is stripped from the insulating substrate 26.